Rename "maint set python auto-load" to "set auto-load-scripts".

	Rename "maint set python auto-load" to "set auto-load-scripts".
	* NEWS: Mention it.
	* python/py-auto-load.c (auto_load_scripts): Renamed from
	gdbpy_auto_load.
	(load_auto_scripts_for_objfile): Update.
	(gdbpy_initialize_auto_load): Rename "maint set python auto-load" to
	"set auto-load-scripts".

	doc/
	* gdb.texinfo (Startup): Document auto-loading of scripts during
	startup.
	(Auto-loading): Delete "maint set python auto-load on|off".
	Add "set auto-load-scripts on|off".